Heavy metal contamination is one of the most important environmental issues. Therefore, appropriate steps need to be taken to reduce heavy metals and metalloids in water to acceptable levels. Several treatment methods have been developed recently to adsorb these pollutants. This paper reviews the ability of residuals generated as a by-product from the water treatment plants to adsorb heavy metals and metalloids from water. Water treatment residuals have great sorption capacities due to their large specific surface area and chemical composition. Sorption capacity is also affected by sorption conditions. A survey of the literature shows that water treatment residuals may be a suitable material for developing an efficient adsorbent for the removal of heavy metals and metalloids from water.

Surfactant-modified clay minerals are known for their good sorption properties of both organic and inorganic compounds from aqueous solutions. However, the current knowledge regarding the effect of both cationic and nonionic surfactants on the properties of bentonite is still insufficient. Bentonite, with montmorillonite as the base clay, was modified with hexadecethyltrimethylammonium bromide (a cationic surfactant) in the amount of 1.0 cation exchange capacity (CEC) of bentonite and varying concentrations of t-octylphenoxypolyethoxyethanol (Triton X-100, a nonionic surfactant). We aimed to improve the understanding of the effect of nonionic and cationic surfactants on clay minerals. The modified bentonites were characterized by X-ray diffraction (XRD), thermogravimetric analysis/differential thermal analysis (TG/DTA), Fourier transform infrared spectrometry (FTIR), field emission scanning electron microscopy (SEM) and specific surface area and pore volume (BET). According to our results, the presence of a cationic surfactant significantly increased the amount of the adsorbed nonionic surfactant. Moreover, an increase in the concentration of nonionic surfactants is also associated with an increase in the effectiveness of the modification process. Our results indicate that the amount of nonionic surfactant used has a significant effect on the properties of the obtained hybrid material. Modification of bentonite with a nonionic surfactant did not cause an expansion of the interlayer space of smectite, regardless of the presence of a cationic surfactant. The modification process was found to significantly decrease the specific surface area of bentonite. Improvement of hydrophobic properties and thermal stability was also observed.

Numerous adsorbents have been introduced to efficiently remove heavy metals and organic dyes from environmental water samples. However, magnetic a porous network aerogels are rarely developed to capture inorganic and organic pollutants from aqueous. We herein fabricated hexagonal boron nitride nanosheets (h-BNNSs)-based on magnetic hybrid aerogels (MHAs) as a lightweight adsorbent for robust uptake of Cr(VI), As(V), methylene blue (MB) and acid orange (AO). The synthetic procedure of poly(ethyleneimine)-modified h-BNNSs (PEI-h-BNNSs) involved thermal poly condensation of melamine and boric acid, pyrolysis of the resultant products which allowed exfoliated by ultra-sonication process further functionalization with PEI-mediated modification of h-BNNSs. The as formed PEI-h-BNNSs allowed in-situ formation of magnetite nanoparticles (Fe₃O₄ NPs) decorated on their surfaces, which are turned to be PEI-h-BNNSs@Fe₃O₄ NPs. The lyophilization treatment of PEI-h-BNNSs@Fe₃O₄ NPs-loaded PVA hydrogels generated the MHAs with large porous structures, diverse and numerous functional groups, good super-paramagnetic and a zero net surface charge. These features enabled the proposed adsorbent (MHAs) to be utilized to efficiently remove Cr(VI), As(V), MB, and AO from an aqueous solution, with maximum adsorption capacity estimated to be 833, 426, 415, 286 mg g⁻¹, respectively. The adsorption kinetics and isotherm data demonstrated that MHAs mediated adsorption of Cr(VI), As(V), MB and AO followed the Freundlich isotherm model and a pseudo-second-order kinetics model. This finding signifies that the MHAs exhibit heterogeneous binding behavior with multilayer chemisorption of Cr(VI), As(V), MB and AO. Subsequently, the practical application were validated by conducting their detoxification of chromium and arsenic in soli-sludge samples.

Zeolites and mesoporous silica materials are effective adsorbents that can be useful for the removal of various pharmaceuticals including non-steroidal anti-inflammatory drugs and antibiotics from low-quality water. This paper summarizes the properties and basic characteristics of zeolites and mesoporous silica materials and reviews the recent studies on the efficacy of the adsorption of selected non-steroidal medicinal products and antibiotics by these adsorbents to assess the potential opportunities and challenges of using them in water treatment. It was found that the adsorption capacity of sorbents with high silica content is related to their surface hydrophobicity (hydrophilicity) and structural features, such as micropore volume and pore size, as well as the properties of the studied medicinal products. This review can be of help to scientists to develop an effective strategy for reducing the amount of these two groups of pharmaceuticals in wastewater.